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Calculation of the due date

by Josephine Andrews
Published: Last Updated on 317 views

The first sign of pregnancy is usually the absence of menstruation . However, this alone is not sufficient evidence of pregnancy. However, if you experience breast tenderness and possibly morning sickness at the same time, there is a good chance that you are indeed expecting a child.

How does the doctor or midwife calculate the time of birth?

Nobody will be able to predict the exact date of birth of your offspring. However, the doctor or midwife is able to limit the time of birth to a large extent. The duration of a pregnancy counts from the first day of the last menstruation – even if the time of conception occurs about 14 days later with ovulation . According to this model, you are already in the third week of pregnancy on the day you became pregnant. A total of about 40 weeks pass before your baby sees the light of day.

To find out the time of delivery, proceed as follows ( calculation according to Naegele’s rule ):

  • Take the first day of your last menstrual period and add a week to it. For example, if the first day of the last rule is April 1st, adding a week will result in April 8th.
  • Now subtract three months, add one year and you have the due date (the date of the expected birth). In our example, that would be January 8 of the next year.

The calculation is only correct if you have had regular menstrual periods about four weeks apart.

However, there are factors that affect the timing of delivery . It is not uncommon for women who stop taking the birth control pill and become pregnant within the next two months to have irregular ovulation. Others, however, have no or only irregular menstruation after stopping the pill . If you don’t have a menstrual period after your last pill bleed but did get pregnant, you should add a week or two to your due date, sometimes more.

In the practice of your gynaecologist there are so-called pregnancy calendars (gravidaria) that you can use to calculate the due date. There are also various apps and other media that can show the probable due date.

Can the doctor decide whether the calculated appointment is correct?

An ultrasound examination in the 9th to 12th week of pregnancy, which your doctor will carry out, provides relative certainty about the time of birth. Based on the size of the embryo and the development data, he will be able to determine the time of delivery very precisely.

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